[unreadable] Synchrotron radiation is an important tool for structural biological studies using X-ray diffraction, X-ray scattering, and X-ray absorption spectroscopy. The quality of data often depends critically on beam spectral quality. The technical limitations (e.g. energy range) of beamlines can make or break experiments. [unreadable] [unreadable] In this application we propose to optimize, design, construct, and test over a wide range of energies a novel, inexpensive, easy to align device ("beam cleaner"). The device has several benefits: improving X-ray beam spectral quality; extending (e.g. tripling) the useful energy range of existing beamlines at third generation synchrotron radiation sources by selecting specific harmonics for experimental use; passively compensating for vertical beam motion as the monochromator angle is changed; and focussing the beam. Beam cleaners offer the potential to simplify new beamline designs by permitting use of channel-cut monochromators in vacuum, followed by a beam cleaner arranged so as to passively compensate for vertical beam motion, without the need for precise in-vacuum mechanics. This device also potentially can be used as a non-beam-hardening variable attenuator for experiments on radiation sensitive biological samples at intense third generation sources, and the devices also appear to be applicable to laboratory research. [unreadable] [unreadable]